The invention relates to a device for pre-heating the intake air or the intake mixture of an internal combustion engine having at least one intake pipe.
It is known from German Utility Model 7,816,169 to preheat the intake air via a heating wire wound around the intake manifold. This device is principally suitable for intake manifolds or intake pipes having a geometrically regular shape, as is the case in manifolds having a circular cross section. However, if the intake air is to be pre heated in a manifold zone in which the contour of the intake manifold is relatively irregular, for example in mixture compressing internal combustion engines in the zone of the fuel injection, continuous contact of the heating wire with the intake-pipe outer surface and thus adequate heat transfer into the wall of the intake pipe can no longer be achieved or, if at all, only at a relatively high cost. In addition, on account of the fact that the heating wire is arranged on the outer surface of the intake manifold, the heat loss to the surrounding area during a heating phase is very high. Furthermore, it is known, in order to pre heat the intake air, to insert an electric heating element into the intake pipe (German Patent Specification 3,426,469); in this case, however, there is a clear reduction in the cross-section of flow.
An object of the invention is therefore to create a device of the type described above with which, without considerably impairing the intake-air or intake mixture flow, low-loss pre-heating of the intake air or the intake mixture can also be achieved in the zones of the intake pipe in which the intake pipe has a geometrically irregular, i.e. a spatially curved, shape.
This object is achieved according to the invention by providing a device for pre-heating in certain zones the intake air or the intake mixture of an internal combustion engine having at least one intake pipe, comprising an electric conductor which, in an active state, delivers resistance heat to the intake air or the intake mixture, the electric conductor being a layer of high electrical resistance applied to one of the inner surface of the intake pipe and the wall of the intake pipe, wherein the layer is a malleable insert of carbon fibers.
With the use of a layer having a high electrical resistance, according to the invention it is possible to also pre-heat the intake air or the intake mixture in such manifold sections which have a geometrically completely irregular shape (spatial curvature).
In preferred embodiments of the invention, a fabric consisting of many individual electric conductors of small diameter can be adapted without problem to the respective inner contour of the manifold. It is thus ensured that the heating facility does not cause any considerable increase in the flow resistance in the intake pipe. The flow in the intake pipe remains completely unaffected if the layer is integrated in the wall of the manifold.
Especially with regard to the flow of the intake gases, it is advantageous in the case of a layer applied to the inner surface of the intake pipe to laminate this layer onto the intake-pipe inner wall, in which arrangement a heat-insulating intermediate layer provided in the zone between the layer and the intake-pipe outer surface keeps the heat transfer via the intake pipe wall to the surrounding area to a minimum. This applies in particular to an intake pipe made of a metallic material. Very rapid vaporization of the fuel injected into the intake pipe of a mixture-compressing internal combustion engine can be achieved if the layer is arranged in the impingement area of the fuel stream.
With carbon fibers as electric conductors, relatively high temperatures can be achieved even with short conductor lengths on account of the high specific resistance of this material. Applied to a fabric made from this material, this means that, related to a certain fabric area and a certain quantity of supplied energy, a relatively low fabric density (packing density) is sufficient to obtain the total resistance of the fabric required to reach a pre determined temperature.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.